Summary
Connection limit issues with Optonline.net recipients are multifaceted, stemming from Optonline's internal policies, infrastructure, and external factors like sender reputation and sending practices. Being a smaller ISP, Optonline has strict connection limits, underfunded sender support, and potentially more aggressive spam filtering. Legacy limits from the dial-up era persist. Shared IP reputation, sudden spikes in email volume, and exceeding connection limits contribute to temporary deferrals or rejections. SMTP servers globally implement connection limits to manage server load and prevent abuse. Maintaining a good sender reputation, complying with bulk sender guidelines, and adjusting sending practices are crucial.
Key findings
- Strict Limits: Optonline has strict connection limits and potentially aggressive spam filtering due to being a smaller ISP.
- Legacy Infrastructure: Optonline's infrastructure and limits are influenced by legacy dial-up era policies.
- Reputation Impact: Shared IP and overall sender reputation greatly impact connection limits; poor reputation leads to stricter limits.
- Volume Sensitivity: Sudden spikes in sending volume can trigger connection limits, resulting in temporary blocks or rate limiting.
- Global Limits: SMTP servers implement connection limits globally to manage server load and prevent abuse.
- Underfunded Support: Optonline is known to have underfunded sender support.
Key considerations
- Monitor & Adjust: Monitor bounce codes and adjust sending behavior to stay within Optonline's limits.
- IP Warm-Up: Warm-up new IPs and gradually increase volume to establish a good reputation.
- Sender Reputation: Prioritize and maintain a good sender reputation through authentication and responsible sending.
- Limit Retries: ESPs should avoid aggressive retries and set initial connection limits low.
- Avoid Spikes: Implement measures to prevent sudden spikes in sending volume.
- Comply with Guidelines: Adhere to bulk sender guidelines to improve deliverability and avoid spam filters.
What email marketers say
9 marketer opinions
Connection limit issues with Optonline.net recipients are primarily caused by Optonline's strict connection policies, often due to being a smaller ISP with limited infrastructure and aggressive spam filtering. Shared IP reputation, sudden spikes in email volume, and exceeding connection limits all contribute to temporary deferrals or rejections. Proper email sending practices and reputation management are crucial.
Key opinions
- Strict Limits: Optonline, as a smaller ISP, enforces strict connection limits and has limited sender support.
- Shared IP Impact: Shared IP reputation significantly affects connection limits; a poor reputation leads to reduced allowances.
- Spike Sensitivity: Sudden spikes in email volume can trigger connection limits, resulting in temporary blocks or rate limiting.
- Aggressive Filtering: Optonline's more aggressive spam filtering can lead to stricter connection limits compared to larger providers.
- Abuse Prevention: Connection limits are also implemented to prevent abuse, server overload, and DOS attacks.
Key considerations
- Monitor Bounce Codes: Regularly monitor bounce codes and adjust sending behavior to avoid exceeding connection limits.
- Warm-Up IPs: Carefully warm-up new IP addresses and gradually increase sending volume to establish a good reputation.
- Sender Reputation: Maintain a good sender reputation through proper authentication and responsible sending practices.
- Connection Settings: Set initial connection limits low to avoid aggressive retries that can exacerbate the issue.
- Avoid Spikes: Implement measures to prevent sudden spikes in email volume that can trigger connection limits.
Marketer view
Email marketer from Email Geeks suggests it sounds like a connection limit issue and asks if there is any idea how many simultaneous connections are being made to their servers.
9 Oct 2021 - Email Geeks
Marketer view
Email marketer from Mailjet explains that ISPs use connection limits to protect their infrastructure from abuse. Sudden spikes in connection attempts from a single IP address can trigger these limits, resulting in temporary blocks or rate limiting.
29 Nov 2022 - Mailjet
What the experts say
3 expert opinions
Connection limit issues with Optonline.net recipients are primarily attributed to the ISP's strict limits, underfunded sender support, and legacy infrastructure. These limitations, originating from the dial-up era and defensive measures due to limited resources, impact legitimate senders.
Key opinions
- Strict Limits: Optonline enforces strict connection limits.
- Underfunded Support: Optonline's sender support is underfunded.
- Legacy Limits: Connection limits persist from the dial-up era to prevent server hosting and bandwidth hogging.
- Limited Infrastructure: Optonline, being a smaller ISP, often has limited infrastructure and less sophisticated spam filtering.
Key considerations
- ESP Adjustment: ESPs should avoid aggressive retries and set connection limits low initially.
- Infrastructure Awareness: Senders should be aware of the limitations of smaller ISPs like Optonline.
- Defensive Measures: Understand that strict connection limits are a defensive measure due to limited resources.
Expert view
Expert from Spam Resource explains that back in the dial-up era, residential ISPs like Optonline implemented strict connection limits to prevent users from running servers and hogging bandwidth. These limits often persist, causing issues for legitimate senders.
3 Aug 2021 - Spam Resource
Expert view
Expert from Word to the Wise shares that smaller ISPs like Optonline often have limited infrastructure and less sophisticated spam filtering systems. This can result in stricter and less transparent connection limits as a defensive measure.
3 Jan 2025 - Word to the Wise
What the documentation says
6 technical articles
Connection limit issues with Optonline.net and other email providers stem from SMTP server implementations to manage load, prevent abuse, and comply with recipient server limits. Poor sender reputation, exceeding rate limits, and ignoring bulk sender guidelines contribute to these issues. Maintaining a good reputation, proper authentication, and responsible sending practices are crucial for avoiding connection problems.
Key findings
- Server Load Management: SMTP servers implement connection limits to manage server load and prevent abuse.
- Connection Throttling: Connection throttling controls concurrent connections to avoid overwhelming recipient servers.
- Reputation Impact: Poor sender reputation leads to stricter connection limits or blocked connections.
- Rate Limiting: Rate limiting policies ensure fair usage and prevent abuse by limiting connections and message sizes.
- Bulk Sender Guidelines: Ignoring bulk sender guidelines results in deliverability issues and potential connection problems.
- Throttling for Protection: Throttling is a safety measure to protect reputations and maintain deliverability rates, with limits on messages per second and daily sending.
Key considerations
- Maintain Reputation: Maintain a good sender reputation through proper authentication and responsible sending practices.
- Comply with Guidelines: Adhere to bulk sender guidelines to ensure emails reach the inbox and avoid spam folders.
- Monitor Sending Limits: Monitor and stay within sending limits to prevent temporary bounces or delivery delays.
- Implement Throttling: Use connection throttling mechanisms to avoid overwhelming recipient servers.
- Address 421/5xx Errors: Address temporary (421) and permanent (5xx) rejection errors by adjusting sending practices.
Technical article
Documentation from Message Systems' PowerMTA User Guide shares that connection throttling is a mechanism to control the number of concurrent connections to a specific domain. It is used to avoid overwhelming recipient servers and to comply with their connection limits, which helps in maintaining a good sender reputation.
22 Jun 2021 - Message Systems
Technical article
Documentation from RFC Editor explains that SMTP servers can implement connection limits to manage server load and prevent abuse. Exceeding these limits can result in temporary rejections (421 errors) or permanent rejections (5xx errors).
22 Jan 2023 - RFC Editor
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